Cell membranes contain specific transport proteins that enable the cell to accumulate growth substrates and pump ions against a concentration gradient. We would like to study the structure and function of a specific active transport system in order to gain some understanding of the mechanism of this process. We will study the maltose/maltodextrin transport system of Escherichia coli. This system is composed of five polypeptides that enable the cell to actively accumulate maltose and longer polymers of glucose (maltodextrins). We will use biochemical techniques to study the oligomeric structure of the three plasma membrane proteins and their disposition in the membrane. Specific antibodies will enable us to detect and purify these proteins. Bacterial strains which overproduce the membrane proteins will be employed. We will also study maltose transport in subcellular vesicles. These experiments will enable us to identify the energy donor compound. The effects of chemical modification reagents will indicate which amino acid residues are important for transport activity. We will also isolate and characterize mutant strains in which the structure and/or function of the transport system has been altered. These will include mutants in which specific portions of each transport protein have been deleted, mutants that are defective in the coupling of energy to active transport, and mutants in which the interaction of substrates with the transport system is defective. Our long term goal is to generate a picture of how substrate molecules interact with these proteins during the process of translocation through the membrane and how metabolic energy is coupled to this process.